This invention relates to suction cleaners and, more particularly, to a safety switch for suction cleaners that automatically varies the speed of the suction cleaner motor in response to different types of attachments that are removably fixed to the body of the cleaner.
Many conventional suction cleaners employ a two-speed motor which is controlled by a manually-operated switch. For cleaning rugs and carpets, a low speed is desired, since the carpet pile or rug tends to block the suction end of the cleaner and may cause a high-speed motor to run hot because of the increased load on the fan. Moreover, if the beater brush is operated at a high speed on a carpet or rug, the suction cleaner wears the carpet pile too fast and the cleaner is difficult to push. A high speed is desirable in applications where dusting attachments are connected to the sweeper, since the ends of these attachments are spaced a considerable distance from the suction fan and a pressure drop occurs along the length of the hose from the dusting nozzle to the sweeper body.
Frequently, the operator becomes confused as to the speed recommended for a particular attachment, particularly in view of the variety of attachments being offered by vacuum cleaner manufacturers. Suction cleaners have been designed, therefore, to include switches which are responsive to a particular attachment. For example, in U.S. Pat. No. 2,072,690, there is disclosed a suction cleaner having a two-speed motor which is operated in response to a switch. The switch, in turn, is a two-position which is actuated to its first position only in response to a dusting attachment, to thereby run the motor at a relatively high speed, and is actuated to its second position only in response to a carpet cleaning nozzle to thereby run the motor at a relatively low speed. Prior art switches of the type shown in U.S. Pat. No. 2,072,690 control the motor speed by a field tap arrangement. One position of such a switch cuts out a portion of the field winding of the motor to permit the motor to run at higher speeds because of the decreased field resistance. The other position of the switch connects the line across the entire field winding to reduce the motor speed because of the increased field resistance.
The conventional switches have met with limited commercial success because of the expense involved in field tap wiring systems. A far simpler wiring arrangement for controlling the speed of a motor is to provide a switch that will connect the field windings in series for low speed operation and that will connect the field windings in parallel for high speed operations. Such a wiring arrangement in its simplest form, however, has not been employed since the field windings are short-circuited and the current is applied directly through the armature if the high speed and low speed switches are intentionally or inadvertently closed at the same time.
To overcome that problem, it has been proposed in U.S. Pat. No. 3,319,282 to employ a simple wiring arrangement and switch that will alternately connect the field windings of a motor in series for low speed cleaning operations in response to low speed cleaning attachments and which will connect the field windings in parallel for high spaced cleaning operations in response to the provision of high speed cleaning attachments on the cleaner. That patent discloses means to permit the alternate operation of the high speed and low speed switches, but prevents the simultaneous operation of both switches.
The object of U.S. Pat. No. 3,319,282 may be defeated, however, if either the high speed or low speed switch is operated intentionally or inadvertently by finger pressure with an attachment off, thus permitting the operator to insert his or her fingers into the fan. With the rise of product liability, therefore, manufacturers are striving for more foolproof safety systems to be built into their products.
It is proposed in a copending application to provide a safety switch which is automatically disconnected to disable the vacuum cleaner before access may be had to the nozzle or accessory attaching means. Thus, before access may be had to the fan, the safety switch must be disconnected from the cleaning attachment.
This is accomplished by mounting the safety switch within the headlight shroud so that when the shroud is in its down or closed position, the safety switch cooperates with lugs on the particular cleaning attachment to drive the motor at either a high or a low speed. In order to remove the attachment, the headlight shroud must be pivoted upwardly to gain access to the connecting lug for the attachment. However, when the headlight shroud is thus opened, the safety switch is disconnected from the attachment, since it is attached to the shroud.
The safety switch itself comprises a housing having spaced electrical contacts along one of its walls. A shiftable contact bar establishes electrical connections between certain pairs of those contacts, and is normally biased to a position wherein electrical connections are not made between the pairs of the contacts. The contact bar has cam surfaces at each end thereof which are adapted to be engaged by lugs which protrude from the attachments. When the contact bar is in its normally biased, first switch position, the motor is disconnected from an electrical circuit. When the contact bar is shifted by one of the lugs to a second contact position, an electrical connection is effected and the motor is run at a relatively low speed. If the lug moves the contact bar to a third switch position, the motor is caused to run at a relatively high speed.
While the switch disclosed in the above mentioned application overcomes many of the problems of the prior art, it has been found that certain problems exist in the operation of the switch. The switch is mounted at a fixed location on the headlight shroud and the attachments are removably attached to the vacuum housing. Due to manufacturing tolerances and wear during use, the lug on the attachment may not move the contact bar the predetermined distance to establish the desired contact. Movement may be too little or there may be overtravel, depending upon the entry axis of the lug in the socket.